.\"	$OpenBSD: ftok.3,v 1.17 2014/11/15 22:22:09 guenther Exp $
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.\" Copyright (c) 1994 SigmaSoft, Th. Lockert <tholo@sigmasoft.com>
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.Dd $Mdocdate: November 15 2014 $
.Dt FTOK 3
.Os
.Sh NAME
.Nm ftok
.Nd create IPC identifier from a pathname
.Sh SYNOPSIS
.In sys/ipc.h
.Ft key_t
.Fn ftok "const char *path" "int id"
.Sh DESCRIPTION
The
.Fn ftok
function attempts to create a unique key suitable for use with the
.Xr msgget 2 ,
.Xr semget 2
and
.Xr shmget 2
functions given the
.Fa path
of an existing file and a user-selectable
.Fa id .
.Pp
The specified
.Fa path
must refer to an existing file that is accessible to the calling process
or the call will fail.
Also, note that links to files will return the same key, given the same
.Fa id .
Only the 8 least significant bits of
.Fa id
are used in the key generation; the rest of the bits are ignored.
.Sh RETURN VALUES
The
.Fn ftok
function will return (key_t)\-1 if
.Fa path
does not exist or if it cannot be accessed by the calling process.
.Sh SEE ALSO
.Xr msgget 2 ,
.Xr semget 2 ,
.Xr shmget 2
.Sh HISTORY
The
.Fn ftok
function originated with System V and is typically used by programs
that use the System V IPC routines.
.Sh AUTHORS
.An Thorsten Lockert Aq Mt tholo@sigmasoft.com
.Sh BUGS
The returned key is computed based on the device and inode of the
specified
.Fa path
in combination with the given
.Fa id .
Thus it is quite possible for the routine to return duplicate keys
given that those fields are not 8- and 16-bit quantities like they
were on System V based systems where this library routine's ancestors
were originally created.
